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WOOD - Roof Repair

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I am working on a project to structurally reinforce an existing church wood
roof.  The clear span of the wood framing is about 36 feet.  The church was
constructed in 1900.  The existing framing consists of 2x8 rafters at 2'-0"
o.c.  The roof pitch is 12:12.  There is a cathedral type ceiling on the
lower part and a collar tie about 6 feet down from the ridge.  There are two
dormers about 8 feet wide for large windows.

The roof has experienced severe sagging over the years and consequently it
has pushed out the top of the 16" stone wall up to about 6 inches.  The jack
rafters on the dormer are single 2x8's, no different from any of the other
rafters.  The dormers are in the middle part of the roof and there are hips
at the building end.  The sagging is most severe at the dormer,    while near
the hips there is very little.  This causes a two way sagging bowl-type
effect at the dormer.

I am using 'A' type frames at about 8 feet on center to stiffen the framing
and control any more movement of the stone wall.  I am also attaching the
existing dormer framing to these 'A' frames to support the dormer.  The
frames will be made from microlam lumber and all construction will be done
from below so that the roof will not be opened up.

My question I would like feedback from the listserver regards jacking up the
roof to install the new frames.  I will need to have the roof jacked up some
because the I want to get the dead weight out of the existing jack rafters
and into the new frames.  The problem I see is popping of the boards of the
roof deck off of the existing rafters.  There is permanent deformation of the
roof boards due to creep, etc.  As the rafts are jacked up it is possible to
pop the board off.  Has anybody developed a good detail to reattach the
boards to the rafters from below the deck?  I could maybe picture some kind
of clip with screws.  The other problem is to know how much to jack the roof.
 I need to minimize it because too much upward movement could cause damage to
the roof.

I would appreciate any feedback from anyone who has done structural repair
work.


__________________________________________________

Richard Lewis, P.E.
Missionary TECH Team
rlewis(--nospam--at)techteam.org

The service mission like-minded Christian organizations
may turn to for technical assistance and know-how.